1. Technical Field
The present invention relates to technology for managing a switching device in network operation.
2. Description of the Related Art
Currently available switching devices have been designed on the assumption that they will be operated in distributed autonomous mode. This is because switching devices are the devices that provide communication accessibility, and because the transfer functionality of a switching device must not come to a stop even if communication with the server managing the switching device should be interrupted. For this reason, switching devices are not designed to operate according to instructions from other devices, but instead to operate based on internal configuration information made in the switching device.
DHCP (Dynamic Host Configuration Protocol) is one means for acquiring and setting external IP addresses for the purpose of enabling communications; however, DHCP can only acquire IP addresses, and cannot acquire all of the information needed for communication with other switching devices.
Another means for enabling communication is automatic learning using ARP (Address Resolution Protocol) or automatic learning of the MAC address belonging to a switching device. Many switching devices have an automatic learning function for learning the MAC addresses for use in communications by Ethernet™; however, owing to existence of VLAN (Virtual Local Area Network) or other technologies for logical division of communications, learning MAC addresses does not automatically mean that communication is possible. For example, if it is attempted to communicate with a switching device connected to a link that belongs to a first VLAN, packets will not arrive where these are from a client terminal or switching device connected to a link belonging to a second VLAN. Moreover, the principal purpose of automatically learning MAC addresses is to minimize broadcasting. Using broadcast packets, a switching device can communicate with other switching devices, servers, and clients whose MAC addresses are unknown to the broadcasting switching device. While the broadcast packets will get through to other switching devices, servers, and client terminals belonging to a given VLAN, they are not transferred to different VLANs. Thus, using broadcast packets, a switching device belonging to a first VLAN will not be able to communicate with a switching device belonging to a second VLAN.
However, where such transfers employ IP addresses rather than MAC addresses, communication among network devices connected to different VLANs will be possible. Such transfers by IP address are possible if routing information has been correctly set in the switching device.
ARP has the same problem described above, since it involves saving associations among IP addresses and MAC addresses, and using the IP address to ascertain the MAC address belonging to a device. That is, even where a switching device uses ARP, if the configuration information of the switching device is not correct, it will not be able to communicate with a device belonging to a different VLAN, despite learning its MAC address.
The range of possible communication among multiple switching devices can be expanded through exchange of mutual authentication information and of routing information they hold. Addresses, identifiers etc. of paired switching devices are set as configuration information in the switching devices. A switching device can communicate with a paired switching device on the basis of the configuration information. In the event that the switching device configuration information is correct, and the network cables or optical fibers have been wired correctly as designed, the switching devices will be able to communicate properly with the paired network device, and initiate exchange of routing information and so on.
LLDP (Link Layer Discovery Protocol), which enables a switching device to transmit its own information unilaterally in order to ascertain the presence of and some information regarding neighboring network devices, is dependent upon configuration information as to sending and receiving of packets from the appropriate port, but is not dependent upon addresses or authentication information of switching devices. For this reason, LLDP is known as a method for ascertaining information of switching devices irrespective of switching device configuration information. Information that can be ascertained through LLDP includes switching device identifiers, and information for physical ports that transmitted packets.
If configuration information in switching devices, such as addresses or identifiers of paired switching devices, have been made in error, communication among switching devices will not be possible. This issue could conceivably be addressed by a method of representing the connection between two switching devices by a “path,” and inputting configuration information relating to the path by way of path information, in order to update configuration information according to the connection between two switching devices. The use of such path information can eliminate setting errors between the two switching devices.
However, while it is possible to make configuration information appropriately in the two switching devices by using correct path information, in the event that the path information is in error, it will of course not be possible to set appropriate configuration information. Moreover, it is difficult to obtain correct path information from configuration information for the two switching devices. The reason is that while information for a paired switching device has been set in the configuration information of a switching device, two potential problems exist, namely, that:    1. the actual physical wiring of network cables or optical fibers may not have been wired correctly as designed; and    2. since switching devices are designed for distributed autonomous operation, it is possible that through direct login to a switching device its configuration may have been changed without regard to paired network devices or to physical wiring. Thus, the configuration information will not necessarily be correct.
Consequently, even if the configuration information includes description of “communications ports of paired devices” and so on, such configuration information may not be reliable for the purpose of creating path information.
In this regard, it would be possible to enable configuration to be made only from a management device, and to disable changes to configuration information made by direct login to switching devices, thereby ensuring the integrity of configuration information. However, by so doing it will no longer be possible to perform a restore operation on a switching device in the event that it can no longer communicate with the management device; therefore, such changes to configuration information through direct login must be permitted. While it would be conceivable to allow changes to be made to configuration information through direct login only in those exceptional instances where communication with the management device is not possible, and to enable configuration to be made only from the management device at other times, this is not really a solution, since the same problem will be confronted when communication with the management device becomes possible.